In recent years, as image quality and precision in copiers and printers have been higher, requirements for the performance of a toner as a developer have been also even severer, and thus a toner having a smaller particle diameter and a sharper particle size distribution with containing no coarse particles and with few fine particles has been being demanded.
Further, as a transferring material for copiers and printers, there has been a need for responding to a variety of materials other than common paper, and the toner has been required to exhibit improved transferring properties. Thus, there have been needs for modifying the surface shape of a toner and further spheroidizing the toner particles.
A method for performing spheroidization and surface modification of a toner includes a method of dispersing and spraying toner particles in hot air by compressed air to perform surface modification and spheroidization (see, Patent Literature 1) and a method of adding an additive such as silica to toner particles and then subjecting the mixture to a heat treatment and fixing the mixture to thereby removing a free additive (see, Patent Literature 2).
However, if excessive heat is applied to a toner in a method of utilizing heat, toner particles coalesce to each other to cause coarse particles.
A spheroidization treatment apparatus has been also proposed in which a colliding member is provided apart from a lower end outlet of a raw material jet port when thermoplastic particles are spheroidized through contact with hot air (see, Patent Literature 3). However, if members in the apparatus receive heat to accumulate heat, a toner is fused to the members which accumulate heat, thereby not enabling stable production. Thus, the apparatus is not preferable in production of a toner.
In order to resolve the above troubles, a spheroidization treatment apparatus has been also proposed which has a configuration in which a raw material-supplying part is provided in the center of the apparatus and a hot air-supplying part is provided outside of the part (see, Patent Literature 4). However, since such a configuration requires providing a plurality of raw material jet nozzles, grows in size in terms of an apparatus configuration and requires compressed gas for supplying a raw material in a more amount, the configuration is not preferable in terms of production energy. In addition, since raw materials are linearly jetted to annular hot air to thereby generate a loss in a treating portion, the configuration is not efficient in increasing an amount to be treated.
In order to improve cleaning properties of a toner, as an apparatus that prevents particles having an extremely high circularity from being generated and enables a uniform and stable heat treatment, a method of providing a plurality of supplying parts to supply powder particles from the outside of hot air has also been studied. However, since the plurality of supplying parts to be usually considered (see, FIG. 9) cause an increase in number of supplying apparatuses by the number of the supplying parts, problems are an increase in space efficiency (occupied area by an apparatus for ensuring a desired amount of production) as well as a decrease in energy efficiency and maintenance load. Further, in the case where variation in amounts to be supplied from the plurality of supplying parts is generated, there is a problem such as an increase in coalesced particles in treating.
In addition, a branching method described in Patent Literature 5 causes a difference in flow speed in a pipe in the case of having no choice but to bend the pipe from the restrictions of layout, and the method has difficulty in uniformity of distribution. In this way, there is room for improvement in a heat treating apparatus in order to efficiently and stably create a toner having a sharp particle size distribution and a low abundance ratio of particles having an extremely high circularity.